Various compositions have been used to coat surfaces exposed to a marine environment, particularly the submerged portions of ocean-going vessels, for the purpose of inhibiting the attachment and growth of barnacles, algae and other organisms responsible for fouling. These compositions usually consist, at least in part, of a film-forming polymer, an organic liquid in which the film-forming polymer is dissolved or dispersed and a toxicant for controlling the fouling organisms. One of the most effective classes of toxicants are triorganotin derivatives of the general formula R.sub.3 SnX or (R.sub.3 Sn).sub.2 Y wherein R represents a hydrocarbon radical, preferably an alkyl radical containing 3 or 4 carbon atoms, and X and Y represent a monovalent and divalent anionic radical, respectively. Bis(tri-n-butyltin) oxide and tributyltin fluoride are illustrative of preferred toxicants.
Recently there has been a trend toward replacing the organic liquids present in prior art antifouling coating compositions with water, which does not present the hazards of flammability and toxicity associated with preparing and applying coating compositions containing organic liquids such as hydrocarbons and ketones as the sole or major solvent for the film-forming polymer. The personnel who apply compositions containing organic solvents are usually required to wear special clothing and respiratory devices to avoid accidental poisoning. In addition, the volatilization of the organic liquid that occurs during drying of the coatings introduces significant amounts of pollutants into the atmosphere. The hazards associated with using coating compositions containing organic solvents increase markedly when the compositions are applied in the form of finely divided sprays, as has become the practice in many shipyards. The use of aqueous compositions has eliminated or at least significantly reduced the flammability and toxicity of organic solvent-containing prior art coating formulations. One disadvantage of aqueous antifouling coating compositions is that they are not compatible with many of the effective triorganotin compounds employed as toxicants in non-aqueous compositions. Addition of the most widely used tripropyltin- and tributyltin compounds, including the halides and oxides, to the aqueous coating compositions usually results in coagulation of the emulsified film-forming polymer, with the result that the composition can no longer be used as a coating material.
One objective of the present invention is to reduce or eliminate many of the hazards, including toxicity and flammability, associated with non-aqueous antifouling coating compositions without sacrificing the effectiveness of these compositions in combating barnacles and other organisms responsible for fouling.
A second objective of this invention is to provide stable, non-flammable aqueous coating compositions that contain at least one triorganotin compound which will inhibit the attachment and growth of fouling organisms.
These objectives, together with others discussed in the following specification, can be achieved using aqueous coating compositions containing an emulsified water insoluble film-forming polymer and an effective amount of a triorganotin compound wherein the hydrocarbon radicals bonded directly to the tin atom are phenyl radicals which may contain one or more inert substituents.